Alternative Firmware (Debian Jessie, Synology DSM6)

Hi,

Somehow after power loss my WDMyCloud-Ex2-Ultra got bricked it had earlier Debian from Fox site installed. Now using uart I’m able to access it and I was following the guide Bricked my EX2. <Also how I unbricked it> - #9 by TCWORLD but I got stuck on “umount /dev/loop0” it shows

umount: /usr/local/modules: device is busy.
(In some cases useful info about processes that use
the device is found by lsof(8) or fuser(1))

Can any of you please advice me how to get back to either original firmware or bring back Debian alive, thanks.